Disk drives are an important data storage technology. Read-write heads are one of the crucial components of a disk drive, directly communicating with a disk surface containing the data storage medium. The invention relates to actively compensating for mechanical strains on the infrastructure holding the read-write head close to the disk surface.
FIG. 1A illustrates a typical prior art high capacity disk drive 10 including actuator 30 with voice coil 32, actuator axis 40, actuator arms 50-58 with head gimbal assembly 60 placed among the disks.
FIG. 1B illustrates a typical prior art high capacity disk drive 10 with head stack assembly 20 including actuator 30 with voice coil 32, actuator axis 40, actuator arms 50-56 and head gimbal assemblies 60-66 with the disks removed.
FIG. 2A illustrates a head gimbal assembly including head suspension assembly 60 with head slider 100 containing the read-write head 200 of the prior art.
Since the 1980's, high capacity disk drives 10 have used voice coil actuators 20-66 to position their read-write heads over specific tracks. The heads 200 are mounted on head sliders 100, which float a small distance off the disk drive surface when in operation. The flotation process is referred to as an air bearing. The air bearing is formed by the read-write heads 200, illustrated in FIGS. 2A, and slider 100, as illustrated in FIGS. 1A-2A.
Often there is one head per head slider for a given disk drive surface. There are usually multiple heads in a single disk drive, but for economic reasons, usually only one voice coil actuator.
Voice coil actuators are further composed of a fixed magnet actuator 20 interacting with a time varying electromagnetic field induced by voice coil 32 to provide a lever action via actuator axis 40. The lever action acts to move actuator arms 50-56, positioning head gimbal assemblies 60-66, and their associated sliders 100 containing read-write heads 200, over specific tracks with speed and accuracy. Actuators 30 are often considered to include voice coil 32, actuator axis 40, actuator arms 50-56 and head gimbal assemblies 60-66. An actuator 30 may have as few as a single actuator arm 50. A single actuator arm 52 may connect with two head gimbal assemblies 62 and 64, each with at least one head slider.
FIG. 2B illustrates the relationship between the principal axis 110 of an actuator arm 50 containing head gimbal assembly 60, which in turn contains slider 100, as found in the prior art.
FIG. 2C illustrates a simplified schematic of a disk drive controller 1000 of the prior art. Disk drive controller 1000 controls an analog read-write interface 220 communicating resistivity found in the spin valve within read-write head 200. Disk drive controller 1000 concurrently controls servo-controller 240 driving voice coil 32, of the voice coil actuator, to position read-write head 200 to access a rotating magnetic disk surface 12 of the prior art.
Analog read-write interface 220 frequently includes a channel interface 222 communicating with pre-amplifier 224. Channel interface 222 receives commands, from embedded disk controller 1000, setting at least the read_bias and write_bias.
Various disk drive analog read-write interfaces 220 may employ either a read current bias or a read voltage bias. By way of example, the resistance of the read head is determined by measuring the voltage drop (V_rd) across the read differential signal pair (r+ and r−) based upon the read bias current setting read_bias, using Ohm's Law.
FIG. 2D illustrates a detailed view head suspension 60 of the prior art.
A prior art head suspension 60 includes suspension load beam 80 mechanically coupled via hinge 82 with extended base plate 84. Head suspension 60 further includes flexure 86, providing electrical interconnections of the read and write differential signal pairs 210, between the disk drive analog interface 220 and read-write head 200 (both in FIG. 2C).
The head gimbal assembly includes head slider 100 rigidly mounted on head suspension 60, with read-write head 200 electrically connected to flexure 86. Head slider 100 is mounted over the right portion of suspension load beam 80 so that read-write head 200 makes contact with flexure 86.
The hinge 82 includes a spring mechanism. Suspension load beam 80, hinge 82 and extended base plate 84 are all typically made from stainless steel. Flexure 86 is a flex printed circuit typically made using polyimide and copper traces.
Both the actuator as a whole and head suspension 60 experience mechanical shock and vibration. However, they do not experience the same shocks and vibrations.
A voice coil actuator, once aligned close to the disk surfaces being accessed, basically has one mechanical degree of freedom, swinging across the plane of the disk, as in FIG. 2B.
By contrast, head suspension 60 faces two mechanical degrees of stress, both vertically in terms of distance from the disk surface 12, as well as, horizontally from the actuator swinging as a whole. The head suspension is trying to maintain a flying height for the slider 100 very close to the disk surface 12, which is rotating at many thousands of RPMs. The suspension mechanism weighs at most a few percent of what an actuator assembly weighs. Any mechanical forces an actuator imparts to a head suspension affect it greatly.
As the actuator swings back and forth seeking different tracks above the rapidly rotating disk surface, the suspension experiences severe mechanical vibrations. The suspension is at the far end of the actuator arm from the pivot and close to the rotating disk surface. The actuator frequently whips the suspension back and forth as it seeks various tracks.
As the move to greater Tracks-Per-Inch continues, these mechanical affects on the head suspension grow in significance. There is increasing need to control suspension resonance.
What is needed is a method of attenuating resonance frequency modes in head suspensions.
Additionally, adding weight to the head suspension adversely affects the actuator as a whole in terms of positioning quickly and accurately above the disk tracks. What is further needed is a way to control resonance frequency modes in a head suspension, without adding any significant weight to the suspension mechanism.
Another problem disk drives face is head suspension shock. During non-operational shock, the read-write head experiences a mechanical shock when it slaps into the disk surface, known as “head slapping”. Head slapping can be quite severe. There is no known practical way to avoid this problem.
What is needed is a way to control the deflection of head from the disk surface. Controlling the disk surface deflection helps minimize the damaging effects of head slapping.
Another problem is at the design phase. Today, modeling is used to predict resonance frequency modes for suspension designs on a component level. But disk drives are complex mechanical systems, which cannot be reliably modeled. This requires actually constructing alternative suspension designs, then assembling, and testing them in disk drives to fully determine the mechanical characteristics such as resonance frequency modes and shock performance.
Selecting a head suspension design must be done for specific disk drive configurations, because there is no way to control and/or predict system level mechanical resonance in these devices. Consequently, head suspension selection requires numerous repeated full systems mechanical tests to select a head suspension design. This is a very costly, time-consuming process.
What is needed is a basic head suspension infrastructure for which vibration resonance can be predictably controlled, minimizing the early system testing of the head suspension mechanism. This reduces the overall design cycle and time to market.
The inventor is aware of only one attempt to actively dampening mechanical vibration in any part of an actuator. In “Active Damping in HDD Actuator”, by Huang, et. al., published March 2001, IEEE Transactions on Magnetics, pages 847-849, an active damping scheme was discussed using strain-type sensors located in the actuator, which provided feedback to control the voice coil of the actuator. Its purpose was to reduce vibration in the actuator's motion in the disk plane as illustrated in FIG. 2B. The approach does not directly help the head suspension's vibration and shock problems. Firstly, it does not sense them, and secondly, the article provided no indication of an active mechanism to dampen head suspension vibrations and shocks.
To summarize, what is needed is a method of attenuating resonance frequency modes in head suspensions, which further, does not significantly increase the weight of the head suspension. What is needed is a way to control the head deflection from the disk surface, which helps minimize damage from head slapping. What is needed is a basic head suspension infrastructure for which vibration resonance can be predictably controlled.